CVE-2026-20796— Time-of-check time-of-use vulnerability in common teams API
Quick assessment
Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.
Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 10.11.9及之前的10.11.x版本存在安全漏洞，该漏洞源于在数据检索时未正确验证频道成员资格，可能导致已停用用户通过竞争条件访问不应知晓的团队名称。
Possible ATT&CK Techniques 1 AI
T1530 · Data from Cloud Storage
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I. Basic Information for CVE-2026-20796
Vulnerability Information
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Vulnerability Title
Time-of-check time-of-use vulnerability in common teams API
Source: CVE Program / CVE List V5
Vulnerability Description
Mattermost versions 10.11.x <= 10.11.9 fail to properly validate channel membership at the time of data retrieval which allows a deactivated user to learn team names they should not have access to via a race condition in the /common_teams API endpoint.. Mattermost Advisory ID: MMSA-2025-00549
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
检查时间与使用时间(TOCTOU)的竞争条件
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 10.11.9及之前的10.11.x版本存在安全漏洞，该漏洞源于在数据检索时未正确验证频道成员资格，可能导致已停用用户通过竞争条件访问不应知晓的团队名称。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)
Affected Products
| Vendor | Product | Affected Versions | CPE | Subscribe |
|---|---|---|---|---|
| Mattermost | Mattermost | 10.11.0 ~ 10.11.9 | - |
|
II. Public POCs for CVE-2026-20796
| # | POC Description | Source Link | Shenlong Link |
|---|
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IV. Related Vulnerabilities
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CVE-2026-18799
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Same weakness: CWE-367
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V. Comments for CVE-2026-20796
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